[GMCnet] Bigger Tires
Jerry Hartley
I just put new tires on my GMC Birchaven. Replaced 225 75R16 with Michelin LTX MS2 235 85 R16. Clearance is definitely an issue. Pictures have been posted on the GMC photo website. The following link should get you there. http://www.gmcmhphotos.com "Bigger Tires" (Someone let me know how to best point to this location). I solved this problem by completing installation of the Quadrabag system. Obviously this would not be a feasible solution if it were the only reason.
I wanted the bigger tires because my Cadillac 500 CID (3.70 final drive) runs 2600 rpm at 60 mph. I don't like the engine noise or the mileage (8.3 mpg). Anyway, it has too much horsepower and too much torque. Yeah, right.
I have read the discussions about tire sizes. How have other people installed these bigger tires? I could not have left the bigger tires on with the original airbags.
Jerry Hartley
Sequim, WA
1977 Birchaven CAD 500/3.70 Final
1976 Royal
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James Hupy
torque & horsepower that the Cad 500 gives you and may even pick up a mile
or two per gallon. Ask around, someone with a 403 might want to trade for
your 3:70. The 403s are an oversquare engine and are happier with a few more
rpms. Good fit for both.
Jim Hupy
Salem, Or
78 Royale 403
Larry
Jerry Hartley wrote on Tue, 30 November 2010 13:01
> I just put new tires on my GMC Birchaven. Replaced 225 75R16 with Michelin LTX MS2 235 85 R16. Clearance is definitely an issue. Pictures have been posted on the GMC photo website. The following link should get you there. http://www.gmcmhphotos.com "Bigger Tires" (Someone let me know how to best point to this location). I solved this problem by completing installation of the Quadrabag system. Obviously this would not be a feasible solution if it were the only reason.
>
> I wanted the bigger tires because my Cadillac 500 CID (3.70 final drive) runs 2600 rpm at 60 mph. I don't like the engine noise or the mileage (8.3 mpg). Anyway, it has too much horsepower and too much torque. Yeah, right.
>
> I have read the discussions about tire sizes. How have other people installed these bigger tires? I could not have left the bigger tires on with the original airbags.
>
> Jerry Hartley
> Sequim, WA
> 1977 Birchaven CAD 500/3.70 Final
> 1976 Royal
Jerry,
I am running a 3.21 and 245's. I figure my FD ratio is somewhere around 3.03. Gives me around 2200 at 60mph and 2600 at 70mph. I've been through the Appalachians towing a 2400lb Tracker with no problems. There are a number of us with the Cad 500 that are running a 3.21 FD. Most of us got a rebuilt unit from John Biwersi. Just seems the right combo for the 500. If you are interested in a 3.21, PM me and I'll pass on contact info.
--
Larry :)
78 Royale w/500 Caddy
Menomonie, WI.
Terrance Boyd
probably the correct tire for the GMC, because it is 1" smaller in diameter
than other brands.So I ordered six, when they came I had them mounted,they
were close to the airbag cone (1/2").
I didn't have any problems with them, but I did notice a drop in
performance. I sat down with paper and pencil (old fashion calculator) and
figured I had loss about 5%. That's when I put in the 321 and regained the
5%, it also put the speedometer right. Trying to keep the speedometer fairly
close I'm now running with 245 75/16. Just rambling.
Terry
John Wright
Here is a real good chart on tire size verses final drive ratios.
http://www.gmceast.com/technical/Brown_Drive_Tire_Ratios.pdf
JR Wright
On Nov 30, 2010, at 7:15 PM, Terrance Boyd wrote:
> I read the GMCMI news letter tha t told me the Goodyear G159 235
> 85/16 was
> probably the correct tire for the GMC, because it is 1" smaller in
> diameter
> than other brands.So I ordered six, when they came I had them
> mounted,they
> were close to the airbag cone (1/2").
> I didn't have any problems with them, but I did notice a drop in
> performance. I sat down with paper and pencil (old fashion
> calculator) and
> figured I had loss about 5%. That's when I put in the 321 and
> regained the
> 5%, it also put the speedometer right. Trying to keep the
> speedometer fairly
> close I'm now running with 245 75/16. Just rambling.
> Terry
>
> On Tue, Nov 30, 2010 at 12:01 PM, Jerry Hartley <jhar...@wavecable.com
> >wrote:
_______________________________________________
Emery Stora
On Nov 30, 2010, at 5:15 PM, Terrance Boyd wrote:
> I read the GMCMI news letter tha t told me the Goodyear G159 235 85/16 was
> probably the correct tire for the GMC, because it is 1" smaller in diameter
> than other brands.
So, when was that published?
Emery Stora
77 Kingsley
Santa Fe, NM
Terrance Boyd
Jim Kanomata
Having sold over 3,000 of them has shown me that you gain power in the
torque range and the load on the engine decreases so the carburetor
runs leaner and the distributor vacuum increases and the timing
advances and improves mileage.
Lot of you drive on the average 50-60 mph. So the rpm is not always in
the torque range where you will benefit.
Other than a brand new engine that is fully computerised from a 2000
year vehicle, you need to get into the 2500 plus rpm to benefit.
I drive hard and travel 65-75mph. I can use any gear I want , but
after try ing everything from 3.21, 3.41, 3.55,3.70, I find that the
3.70 gives me the mileage and performance.
I have a CAD 540 bored and stroked, port injected and twin turbo ed
engine and pull 7.5-8 mpg pulling Graces Oldsmobile van which scales
in at over 6,000 lbs.
When I'm not towing I will get 8-10 as I drive 70-80mph.
It takes tremendous power to push against the wind.
Don't tell me you have so much torque that you need to gear up to a
higher ratio.
If your engine makes noise, your engine compartment needs to be gasket properly.
If your mileage suffers,check the mechanical advance and the vac
module along with the carb.
80% of the people that went to the 3.70 will tell me that the mileage
did not change and the power went up.
I have a friends that run our 4.10 gears at 55mph and tell me they get 12mpg.
Before that they ran a 3.55 and were getting 8mpg.
--
Jim Kanomata
Applied/GMC, Fremont,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
Jim Kanomata
There is something wrong withyour ignition system if thatis all you
can get out of your Cad.
I can work out a sweet deal if you want to try a 3,55.
Call me. (800)752-7502
On Tue, Nov 30, 2010 at 11:01 AM, Jerry Hartley <jhar...@wavecable.com> wrote:
>
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
Emery Stora
On Nov 30, 2010, at 5:15 PM, Terrance Boyd wrote:
> I read the GMCMI news letter tha t told me the Goodyear G159 235 85/16 was
> probably the correct tire for the GMC, because it is 1" smaller in diameter
> than other brands.So I ordered six, when they came I had them mounted,they
> were close to the airbag cone (1/2").
> I didn't have any problems with them, but I did notice a drop in
> performance. I sat down with paper and pencil (old fashion calculator) and
> figured I had loss about 5%. That's when I put in the 321 and regained the
> 5%, it also put the speedometer right. Trying to keep the speedometer fairly
> close I'm now running with 245 75/16. Just rambling.
> Terry
>
That information was from an old GMCMI newsletter #35 dated back to 1991.
A careful read of that information would show that the member said it was only for a Goodyear Unisteel tire which I do not believe is still made in that size..
The article goes on to say that "almost all brand names of the LT235/85R15 are at least 1" larger than the 9.50 tires which makes them unsuitable for the GMC".
Tires have changed a lot in the last 19 years since the information was submitted by a member.
Especially with tires one should not go by information that old.
Emery Stora
77 Kingsley
Santa Fe, NM
Terrance Boyd
85/16 size. But when I put them on in1993 they were.
Terry
Emery Stora
that you can stop worrying about the size now since it's 17 years
since you bought them.
I assume that you are no longer using them. -- I HOPE!
Emery Stora
Jim Galbavy
In most cases it is a clearance problem. Tires that are too wide or to tall will hit on the body / frame or suspension. This can cause problems with the front end when making turn or overall just when going over bumps. Think of the problems of a "Low rider".
jim galbavy
'73 X-CL ANNIE
Chesterfield, Va / Lake Mary, Fl
Hardie Johnson
AnnabelleR wrote on Thu, 02 December 2010 06:25
> I have a question regarding bigger tires <> What's the difference if cars have bigger tires? For example, I notice sports cars usually have 17- or 18-inch tires. "Ordinary" cars usually have 15-inch tires. Upper trim levels of these cars get bigger tires. I heard bigger tires enable a car to go a further distance in a same amount of time, because of the bigger circumferences. Bigger tires can stop a car better because of wider surface contact. But bigger tires need more gas, possibly more road noise. What are all the pros and cons of bigger versus "normal"-size tires?
The cars you see with large diameter _wheels_ have low profile ratio _tires_ and the rolling diameter nets out about the same. While this makes for a cool look, it is inefficient because heavy metal wheel has replaced lighter rubber. Most cars today have 16" wheels, higher performance cars have larger diameter wheels.
Bigger tires don't, "enable a car to go a further distance in a same amount of time", pushing on the accelerator does that - you go faster. Bigger tires allow the engine to rotate slower at a given speed.
With our coaches the problem is it is not easy to find tires for the original 16.5" wheels so many have switched to a more standard 16.0" wheel. Also, the first batch of GMC wheels were not suitable for modern radial tires.
This change of tire (not the wheel) has an effect on the rolling radius and will throw off the calibration of the speedometer.
The stock 3.07 final drive ratio is low and luggs the engine, so one way to deal with this is to go with a 16.0" tire with a low profile. This will give a harsher ride. I am not sure why someone would put on a larger tire as this makes to lugging worse. Maybe it is related to load capacity, which is a BIG concern for our coaches ??
The solution is to go with a tire that is the same outside diameter as original, and install a higher numerical ratio final drive.
The fuel economy does not suffer because, over a range of rpm, the engine delivers, more or less, the same power and consumes the same fuel at a given highway speed. A higher numerical ratio allows the engine to operate more efficiently, especially on acceleration, and fuel economy may improve.
As for the speedo, check and calibrate and adjust the gearing, or rely on your GPS.
"Not 'all' the pros and cons of bigger tires."
--
Hardie Johnson "Crashj"
1973 26 foot Glacier, White Thing
Raleigh NC
Rob Mueller
I would suggest you visit your local tire shop and ask them these questions
or try Google.
Good luck,
Rob M.
USAussie
-----Original Message-----
From: gmclist...@temp.gmcnet.org
[mailto:gmclist...@temp.gmcnet.org] On Behalf Of Annabelle
Sent: Thursday, December 02, 2010 5:26 AM
To: gmc...@temp.gmcnet.org
Subject: Re: [GMCnet] Bigger Tires
Hello,
I have a question regarding bigger tires and i hope you will let me know
about it.The question is What's the difference if cars have bigger tires?
For example, I notice sports cars usually have 17- or 18-inch tires.
"Ordinary" cars usually have 15-inch tires. Upper trim levels of these cars
get bigger tires. I heard bigger tires enable a car to go a further distance
in a same amount of time, because of the bigger circumferences. Bigger tires
can stop a car better because of wider surface contact. But bigger tires
need more gas, possibly more road noise. What are all the pros and cons of
bigger versus "normal"-size tires?
Thanks in advance.
Ali
D C *Mac* Macdonald
As someone else has stated, the "premium" wheels
on higher-end autos (and trucks) wear much lower
profile tires to basically keep close to the same
running diameter (and engine RPM). These lower
profile tires have considerably lower (and stiffer)
sidewalls which will normally improve handling and
steering response.
All things being equal, the ride comfort will suffer
and with the greater tread width, will hydroplane
more easily with water on the road surface.
I believe "standard" auto tires these days wear a
75% to 78% profile ratio. "Performance" tires are
now available with as low as 25 or 30 percent for
the maximum possible grip in turns.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ ex-Palm Beach, 76 ~ ~ ~
~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
----------------------------------------
> From: robmu...@iinet.net.au
> To: gmc...@temp.gmcnet.org
> Date: Thu, 2 Dec 2010 08:08:19 -0600
Les Burt
larger tire is due to availability and commonality.
The larger 235/85-16 is a very common tire on today's 3/4 & 1 ton trucks. You
can find lots of them just about anywhere tires are sold. The correct size
225/75-16 is less common, but still easily found in most tire stores today.
Going to a tire with a higher aspect ratio(the 2nd number in the size) MAY
affect ride quality, handling, & vehicle stability, either positively or
negatively due to the taller sidewall. It all depends on the quality & specs of
the tire you choose as well as the inflation pressures you choose to run. Larger
tires also typically have a higher weight carrying capacity. The tendancy might
be to run lower pressures with the larger tires, but that can have a negative
affect on vehicle stability.
Choose your tire brand and size carefully. Straying away from what is known to
work well is putting your travelling fun in jeopardy.
Thanks,
Les Burt
________________________________
From: Annabelle <who...@live.com>
To: gmc...@temp.gmcnet.org
Sent: Thu, December 2, 2010 6:25:34 AM
Richard Brown
Personally, I'm a believer in the idea that a vehicle should stop better than is runs. Every inch of stopping distance reduced counts.
Richard & Carol Brown
PO Box 941
Lindale, TX. 75771
1974 GMC Eleganza SE (DILLIGAF)
Gary Casey
With regard to larger diameter rims, what you said is about the long and short
of it. It started as a way to increase brake diameter, but progressed into a
style thing. I think the huge oversize tire (I think some are approaching 30
inches) it is strictly style and the tires have such little sidewall the ride
must be terrible. And I'm told that as the tire aspect ratio gets down to 45 or
less, the wheels are very susceptible to impact damage from curbs or chuckholes.
But, unless the owner is a serious enthusiast, I don't think larger brakes are
typically fitted inside larger tires. And the diameter of the brake rotor has
very little to do with stopping distance as long as the brake is capable of
locking the wheels. It has everything to do with resisting fade from repeated
stops, though.
And from the tone of your comment I assume that you assume that the outside
diameter (some call it the "rolling radius") stays the same. In our coaches
there is not much room for a larger diameter tire. I have 3 sizes on mine (some
would say that's not the best arrangement, and I would agree!). The 225/75-16
is about the same diameter as the 8.75-16.5, but the 215/85-16 is almost an inch
larger in diameter than the others. It does not make a good fit in the rear. I
would suggest that if one wants to change the effective gearing he looks for
another way than changing tire diameter.
Gary Casey
I have asked that question, myself. Here's the answer I got. It was originally
done on Formula 1 cars to allow the use of larger brakes to be fitted.Other
types of racing followed suit. Some people put them on for looks, but the only
practical reason to fit them is to allow bigger disc brake rotors to be fitted
while keeping tire diameter within reason with low-profile tires. Ride quality
sucks with low-profile tires, but handling improves up to a point because
shorter sidewalls deflect less in corners. I think that 90% of the big rims are
fitted for looks, but it started out as a practical solution to a problem.
?? Personally, I'm a believer in the idea that a vehicle should stop better than
is runs. Every inch of stopping distance reduced counts.
Richard & Carol Brown
Rob Mueller
I reckon the Escalades, Navigators, and Big Pickups with huge wheels and
standard brake rotors look absolutely ridiculous!
I reckon it goes along with people that like to drive HUGE vehicles like
this to impress people!
Their vehicles scream "LOOK AT ME! LOOK AT ME! LOOK AT ME!
Regards,
Rob M.
USAussie
-----Original Message-----
From: gmclist...@temp.gmcnet.org
[mailto:gmclist...@temp.gmcnet.org] On Behalf Of Richard Brown
Sent: Thursday, December 02, 2010 2:06 PM
To: gmc...@temp.gmcnet.org
Subject: Re: [GMCnet] Bigger Tires
Ken Henderson
Another problem with low profile tires that no one's mentioned is wheel
damage. I visited "my" welder yesterday and found him, as I often do,
welding a wheel which had road damage. That one was probably 10" wide, with
about 8" of offset. Right in the center between the rims was a big "star
burst" hole from hitting a rock or other debris. More common is chunks out
of the rims. The deflection available with low profile tires simply doesn't
provide much protection for the wheels.
Since we have an unusually large proportion of "...LOOK AT ME.." cars here,
There are almost always a couple fancy wheels in the shop awaiting repair.
$50-$100 for repairing a $300-$500 wheel isn't my idea of stylish -- not to
mention the inevitably destroyed tire.
Ken H.
On Thu, Dec 2, 2010 at 8:01 PM, Rob Mueller <robmu...@iinet.net.au> wrote:
> ...
I reckon the Escalades, Navigators, and Big Pickups with huge wheels and
> standard brake rotors look absolutely ridiculous!
>
> I reckon it goes along with people that like to drive HUGE vehicles like
> this to impress people!
>
> Their vehicles scream "LOOK AT ME! LOOK AT ME! LOOK AT ME!
>
>
Stick Miller
Oversize tires have so far cost me an airbag and 2 T-Skirts. The airbag was my fault as a newbie. I did not level the coach properly and took a turn with a dip I shouldn't have attempetd. The tire rubbed a hole in a perfectly good airbag. That alone could have been prevented with proper leveling and a more knowledgable owner and a different route.
The T-Skirts are a different issue. When the coach is lowered in the rear for any reason the tires rest on or very near the T-skirts unless watched carefully. Clearance is very tight at ride height and as a result the T-skirts are ragged along points of contact. I'm not letting them touch any more, but I'm also not able to lower as much as I'd like for draining the fresh water.
I will go with original size tires in future purchases.
By the way, my father's company (he was the President) bought a GMC motorhome new, probably in '74 or '75. When it came in my mother refused to accept it because it didn't have white sidewall tires and no "respectable woman is going to ride in a vehicle with blackwalls."
It's funny how tastes change. I have trouble finding any brand of whitewalls for my '96 Cadillac Fleetwood. I have 3 year old Khumos now and I'm not sure what I'll do when the time comes to replace them. All I know is that that car sure doesn't look right without them.
--
Stick (I used to be skinny) Miller
'78 Royale
Americus, Georgia
http://www.gmcmhphotos.com/photos/showphoto.php?photo=35133
Don Adams
Stick, white walls are easy to find for older, "vintage" cars.
Wallace Wade in Dallas 214-688-0091 carries many sizes. Cooper and others still make them. He also carries Red Lines for muscle cars. A google search might find you a source in Atlanta, or call Wallace maybe he will.
--
Don
67 Datsun 2000
78 Suzuki 400
Shan Rose
I think the only way to avoid clearance issues in the rear with larger tires is to go with the 4 bager system, since it raises the height of the rear just a tad to take up the slack from the extra 3/4 tire diameter. I know the stock tires on an early coach sit on the wheel wells. I just bought a set of 225 dunlop's so hopefully no issues with them..
larry erd
David L Greenberg
On Fri, 3 Dec 2010 21:44:44 -0500 larry erd <1lj...@gmail.com> writes:
> Coker Tires has them.
>
> On Fri, Dec 3, 2010 at 12:05 PM, Don Adams <dj.a...@att.net>
> wrote:
>
> >
> >
> >
> > Stick, white walls are easy to find for older, "vintage" cars.
> > Wallace Wade in Dallas 214-688-0091 carries many sizes. Cooper
> and others
> > still make them. He also carries Red Lines for muscle cars. A
> google search
> > might find you a source in Atlanta, or call Wallace maybe he
> will.
> > --
> > Don
> > 67 Datsun 2000
> > 78 Suzuki 400
> >
I have Coker WWWs on my Packard but they run about $200 apiece plus
installation costs.
I haven't seen any white wall tires on any GMCs since the 70s! I never
replaced my OEM tires, on my 1st GMC, with WWs when they were recalled.
Just keeping the coach clean was enough.
David Lee Greenberg
Port St Lucie, FL skype: david.lee.greenberg
Dedicated to the Preservation of the Classic GMC Motorhome
http://GMCmhRegistry.com
http://www.picturetrail.com/gmcregistry
____________________________________________________________
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Grant Funding May Be Available to Those Who Qualify!
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Stick Miller
Thanks - I'm familiar with classic and antique car tires. This is a '96 and as inconcievable as it might seem, it is the car I drive every day. I just turned 100K miles and it still looks better than the cookie cutter stuff they turn out today. I don't want wide whitewalls and I don't want to pay $200 a piece for tires. I bought the Kumos from Tire rack but last time I checked they didn't have anything in my size to replace. I'd go for a premium tire as a last resort but not looking for a "gangster wall". A 1/2" ribbon whitewall will do nicely. I'm in good shape for now.
Thanks for the suggestions.
--
Stick (I used to be skinny) Miller
'78 Royale
Americus, Georgia
http://www.gmcmhphotos.com/photos/showphoto.php?photo=35133
Don Adams
[quote title=Stick Miller wrote... I have trouble finding any brand of whitewalls for my '96 Cadillac Fleetwood...
I'm in good shape for now. ...
Thanks for the suggestions. [/quote]
I understand you don't consider your '96 to be classic or antique, just your kinda car. That size tire was used on many vehicles and while I'm a big fan of Discount Tire, there are many other sources for low demand tires with wide, narrow, red or yellow sidewalls. Maybe not as cheap as imported Kumo's but you never know. Your in good shape now, but you brought up having trouble finding whitewalls. Just trying to help.
--
Don
67 Datsun 2000
78 Suzuki 400
_______________________________________________
Stick Miller
Thanks, again. I hope I'll be able to keep the look when the time comes.
--
Stick (I used to be skinny) Miller
'78 Royale
Americus, Georgia
http://www.gmcmhphotos.com/photos/showphoto.php?photo=35133